1. Field of the Invention
The present invention relates generally to devices for operating on wells, such as in workover operations. More specifically, the present invention relates to coiled tubing systems for injecting and extracting continuous lengths of tubing into and out of wells in various well servicing operations.
2Description of the Prior Art
Various tubing systems are shown in the prior art for working on wells. Generally speaking, a continuous metal tubing is driven down the well bore by means of an injector head. In the prior art devices, a pair of continuous-chain tube gripping assemblies were motor driven in the injector head to grip the tubing and move it down the well bore. Reverse operation of the gripping assemblies was used to withdraw the tubing string from the well bore. At the surface, the tubing was stored on a large drum or reel from which the tubing was withdrawn by the pull of the injector head. The reel was motor driven to rewind the tubing as it was withdrawn from the well.
The prior art coiled tubing systems utilized opposing chain designs in which a plurality of gripper members were carried by the opposing chains, the grippers being frictionally driven to engage a selected length of tubing for injecting the tubing with the well bore.
The prior art designs suffered from a number of disadvantages. The opposing chain drive design could not be easily removed from the selected length of tubing being inserted within the well bore if problems occurred during the well working operation. As a result, it was usually necessary to cut the tubing at the well surface with the result being a weakened section of the tubing string. The opposing chain drive designs satisfactorily gripped smaller diameter tubing such as one inch tubing but were not well adapted for gripping larger diameter tubing. The prior art systems also required a large number of working parts which increased maintenance and operating costs. Because the opposing grippers were formed with jaw openings of fixed diameter, it was not easy to retrofit the injector head for a different size diameter of coil tubing in the field. It was also difficult to prevent wear to high dollar component parts of the prior art devices such as the fixed diameter grippers.
A need exists for an improved coil tubing injector unit which would accommodate larger diameter tubing and which could be readily refitted in the field to accommodate a variety of tubing sizes.
A need also exists for such an injector unit which would feature fewer moving parts and lower maintenance costs as compared to currently available units.
A need also exists for such an improved injector unit which would feature an open face design to allow the unit to be easily removed from a string of tubing being injected into a well should the need arise.